As a thermoplastic polyester elastomer, elastomers which comprise a crystalline polyester such as polybutylene terephthalate (PBT), and polybutylene naphthalate (PBN) as a hard segment and a polyoxyalkylene glycol such as polytetramethylene glycol (PTMG) and the like and/or polyester such as polycaprolactone (PCL), polybutylene adipate (PBA) and the like as a soft segment are conventionally known and practically used (See, for example, Patent Documents 1 and 2).
However, it is known in the art that polyester polyether-type elastomers comprising a polyoxyalkylene glycol as a soft segment are excellent in water resistance and low-temperature properties but poor in heat-aging resistance and that polyester polyester-type elastomers comprising polyester as soft segment are excellent in heat-aging resistance but poor in water resistance and low-temperature properties.
In order to solve the above-mentioned shortcomings, polyester polycarbonate-type elastomers comprising polycarbonate as a soft segment have been proposed (See, for example, Patent Documents 3-8).
Although the polyester polycarbonate-type elastomers disclosed in these Patent Documents can solve the above-mentioned problems, a problem remains that obtained polyester polycarbonate-type elastomers are poor in block order and an ability to retain block order when the polyester polycarbonate-type elastomers are kept in a molten state (hereinafter, simply referred to as “block order-retaining ability”) because a molecular weight of polycarbonate diol used as a raw material is low, and others.
For example, low block order causes a problem that a melting point of a polyester polycarbonate-type elastomer becomes lower. Thus, in applications, for example, where joint boots, wire coating materials are used under high-temperature circumstances such as on the periphery of automobile engines, low heat resistance may be problem. Patent Documents 4, 7 and 8 disclose that a melting point can be raised by introducing a naphthalate backbone as a polyester component. However, since introducing a naphthalate backbone is expensive, it is desired to raise a melting point by introducing a polyester component having an inexpensive terephthalate backbone. In addition, for a polyester polycarbonate-type elastomer comprising a polyester component having a naphthalate backbone, it is desired that its melting point is further raised in order to compensate cost increasing.
In addition, recently it is demanded to reuse irregular products and recycle merchandise from viewpoints of environmental burden and cost reduction. High block order-retaining ability is necessary for satisfying the above demand. Based on the background, it is strongly demanded to develop a polyester polycarbonate-type elastomer having a high block order and excellent block order-retaining ability.
On the other hand, Patent Documents 7 and 8 disclose methods for producing polyester elastomers by reacting a polyester component constituting a hard segment and a polycarbonate diol component constituting a soft segment in a molten state to prepare a block polymer and by increasing its molecular weight with a chain extending agent. This method for producing is effective to increase a molecular weight of the block polymer. However, since the block order and block order-retaining ability are greatly affected by a reaction process mainly for preparing the block polymer, it is difficult to improve the block order and block order-retaining ability by a method which prepares the block polymer followed by increasing its molecular weight with a chain extending agent. Accordingly, the prior art have not provided a thermoplastic polyester elastomer having the above preferred characteristics. Therefore, it is strongly desired to establish a method for producing a polyester polycarbonate-type elastomer for economically producing a thermoplastic polyester elastomer having the above preferred characteristics.
[Patent Document 1] JP H10-17657A
[Patent Document 2] JP 2003-192778A
[Patent Document 3] JP H07-39480A
[Patent Document 4] JP H05-295094A
[Patent Document 5] JP H06-306262A
[Patent Document 6] JP H10-182782A
[Patent Document 7] JP 2001-206939A
[Patent Document 8] JP 2001-240663A